Coated electrical conductors typically comprise one or more electrical insulation layers, also referred to as wire enamel compositions, formed around a conductive core. Magnet wire is one form of coated electrical conductor in which the conductive core is a copper wire, and the insulation layer or layers comprise dielectric materials, such as polymeric resins, coated peripherally around the copper wire. Magnet wire is used in the electromagnet windings of transformers, electric motors, and the like. Because of its use in such windings, the insulation system of magnet wire must be sufficiently flexible such that the insulation does not delaminate or crack or otherwise suffer damage during winding operations. The insulation system must also be sufficiently abrasion resistant so that the outer surface of the system can survive the friction, scraping and abrading forces that can be encountered during winding operations. The insulation system also must be sufficiently durable and resistive to degradation so that insulative properties are maintained over a long period of time.
The insulation layer or layers of coated conductors may fail as a result of the destructive effects caused by corona discharge. Corona discharge is a phenomenon particularly evident in high voltage environments, such as the electromagnet wire windings of electric motors and the like. Corona discharge occurs when conductors and dielectric materials are subjected to voltages above the corona starting voltage. Corona discharge ionizes oxygen to form ozone. The resultant ozone tends to attack the polymeric materials used to form conductor insulation layers, effectively destroying the insulation characteristics of such insulation in the region of the attack. Accordingly, electrical conductors coated with polymeric insulation layers are desirably protected against the destructive effects of corona discharge.